As a substrate for a reflective mirror of a general rear projection television (RPTV), a float glass plate of a board thickness of 3 to 5 mm is used. The float glass plate has waves in the direction perpendicular to the flow direction of the float, and the wave continues in the direction of the flow of the float. More specifically, on the float glass plate, a streaked pattern (microscopic wavy irregularities) is formed in the direction parallel to the flow direction of the float. The microscopic wavy irregularity has an influence on the optical uniformity of the surface reflection. Therefore, when a number of irregularities are formed on a float glass plate, streaked unevenness (light and dark pattern) due to high and low intensities of light may be formed on the reflected image. An MTF method for determining whether or not a streaked light and dark pattern is formed on the reflected image of a float glass plate by quantitatively extracting the distortion of the reflected image and evaluating it, and the total visual inspection for determining whether or not all float glass plates reach the good item reference level by visually determining the reflected images which are actually projected are carried out. As the result of these evaluations, it has been found out that matching the flow direction of the float with the wide angle diffusion direction of the projection system brings about a good result in the visual inspection.
Thus, the display performance of rear projection televisions (RPTV) is maintained by carrying out total visual inspection of the reflected images actually projected after carrying out the draw line control which makes the wide angle diffusion direction of the projection system, namely, the long side direction of the float glass plate, and the flow direction of the float parallel to each other, for the float glass plates for use in the reflective mirrors of the rear projection televisions (RPTV).
Further, it is already disclosed that in the reflective mirror for use in a rear projection type display or the like, at least one surface of a glass substrate is polished so as to have a predetermined surface roughness (0.05 μm or less under the measurement condition of the cutoff value of 0.8 mm to 8 mm) (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 2001-235798).
Meanwhile, as a glass substrate for use in a liquid crystal panel, a float glass plate of a plate thickness of 0.2 to 1.1 mm (±0.1 mm) is usually used. When a liquid crystal panel is manufactured by using the float glass plate as the glass substrate, color unevenness may occur to the liquid crystal panel due to the abovementioned wave. Therefore, in order that the liquid crystal panels reach the good item reference level, inspection of the quality of the glass substrates for use in the liquid crystal panels is carried out.
However, the abovementioned total visual inspection is generally carried out by making white display by placing a reflective mirror in the projection system of a rear projection television (RPTV) and by an inspector observing the light and dark patterns on the screen at a predetermined distance to make judgment of presence or absence of a streaked pattern, and therefore, the inspection depends on the visual acuity and memory of the inspector. Therefore, the good item reference level is likely to vary depending on daily change in the conditions, and the quality of the float glass plate cannot be quantified. Thus, it is necessary to set the good item reference level to be higher, and excessively high quality is brought about.
Further, in order to perform the total visual inspection, the number of the projection systems of rear projection televisions (RPTV) has to be increased in accordance with increase in the number of objects to be inspected. Therefore, the capital investment and human cost increase, and cost reduction by mass production cannot be carried out to result in cost increase.
Further, the draw line control needs to match the flow direction of the float glass plate with the long side direction of the float glass plate, and therefore, the degree of freedom of glass cutting decreases. As a result, yield reduces and cost increases as compared with the case in which the draw line control is not carried out.
Meanwhile, in the liquid crystal panels, color unevenness sometimes occurs even in the liquid crystal panels using the glass substrates determined to be within the standard in the index (for example, amplitude) of the quality inspection of the glass substrate used at present, or color unevenness does not sometimes occur even in the liquid crystal panels using the glass substrates which are determined as non-standard, and the index of the quality inspection and the good item reference level of the liquid crystal panel do not correspond to each other.
Therefore, in order to manufacture the liquid crystal panels at the good item reference level reliably, excessive polishing needs to be performed for the float glass plates, as a result of which, tact time becomes long, and cost increases.
The invention is made in view of the problems as above. An object of the invention is to provide a glass substrate for a reflective mirror, the reflective mirror including the glass substrate, a glass substrate for a liquid crystal panel and a liquid crystal panel including the glass substrate, which secure display quality by quantitative control and can reduce control cost and manufacturing cost.